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BoTANTicAi. Museum Leaflets Vol. 28, No. 1 

March 1980 



LEAF VARIATION AMONG CANNABIS SPECIES 

FROM A CONTROLLED GARDEN 

LoRAN C. Anderson^ 

The genus Cannabis has had a long association with man and 
contains considerable variation in growth form, achene size, and 
chemical content. The variation has taxonomically been 
variously interpreted. Some maintain the genus is polytypic with 
at least three species (Emboden, 1974; Schultes et al, 1974). 
Others (Small and Cronquist, 1976) believe that it is properly 
viewed as monotypic: i.e. limited to C. saliva L. They do, 
however, recognize several infraspecific varieties. 

Historical aspects and rationale for the different treatments are 
amply covered in these papers. 

My work on wood anatomy (Anderson, 1974) supported the 
polytypic generic concept. A controlled garden (2.6 acres) is 
maintained at the University of Mississippi by the School of 
Pharmacy for the National Institute on Drug Abuse where 
collections from throughout the world are propagated. In 1976, 1 
visited the facility several times to obtain additional vouchered 
wood samples from plants grown in a uniform garden. While 
gathering the Cannabis samples, 1 became aware of differences in 
leaf morphology. Variation in garden-grown plants has already 
been noted by Quimby et al. (1973), but they did not quantify 
their data. This report analyzes leaf form in Cannabis and 
compares the variation in relation to the alternative taxonomic 
treatments. 

METHODS AND MATERIALS 

Measurements were made from the largest leaf on each voucher 
specimen. Dimensional data were taken from the central (longest) 
leaflet. Measurements as illustrated in Fig. 1 included leaflet 



' Deparlment of Biological Science. Florida State University, Tallahassee, Florida and 
Associate in Fconomic Plant Morphology in the Botanical Museum. Harvard University. 



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length (L), leaflet width and length to the widest point. Ratios of 
width to length (W/L) and length to widest point to total length 
(WP/L) were determined. Leaflet number, plant height and sex 
of the sample were also recorded. 

Statistical analyses were made with assistance from Dr. David 
Schrader; these analyses of all materials are on file at Florida 
State University. Ken Womble and Melanie Darst helped with 
graphics. 

A total of 377 samples were measured. Most materials came 
from the Mississippi garden. The University of Mississippi 
School of Pharmacy and Dr. C. E. Turner are thanked for 
making their facilities and the plants available. Some garden 
plantings were maintained for several generations: therefore, 
samples were taken only from original seed sources to prevent 
possibility of garden hybridizations. 1 collected sixty specimens 
representing thirty-nine different seed sources. That somewhat 
extensive population sample was augmented by the intensive 
sampling from the garden in 1972 by Dr. R. E. Schultes and his 
colleagues (with 237 specimens from thirty-two seed sources). 
Vouchers are preseved at the Florida State University and the 
Botanical Museum of Harvard University, respectively. An 
additional eighty specimens from different wild or naturalized 
populations were studied at the Gray Herbarium and Arnold 
Arboretum. 



RESULTS 

Samples were placed in four categories based mainly on growth 
form. The three major forms are illustrated in Fig. 2. Those 
classed as C sativa were taken from tall, laxly branched plants {S, 
in the tables). Relatively tall plants with very narrow leaflets and 
small achenes were classed as C. sativa, small-seeded (SS); short, 
compact plants that were densely branched were classed as C. 
indica Lam. (I); and those mature plants that were two feet tall or 
less and unbranched, as C ruderalis Janisch. (R). 

Mean data for leaf morphology for the four categories and 
three collection sets are given in Table I. The four categories in 
my 1976 sampling were all significantly different for W/L and 

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WP/L at the 99.9% level of confidence, as determined by a 
Student's /-test. Statistical analyses were not made on the other 
sets, due partly to absence of garden material of C ruderalis in 
1972. 

Garden plants maintained their relative growth patterns: i.e., 
height and branching; but leaves were noticeably larger under 
cuhivation (compare 1976 and 1972 versus "wild" in Table 1). 
Although leaves were larger, dimensional ratios of the central 
leaflet (W/L and WP/L) did not vary significantly between 
garden-grown and wild samples. 

Massed data for all three collection groupings are given for the 
four categories in Table 2. None of these categories is significantly 
distinct for leaflet length, although C. ruderalis consistantly has 
small leaves. The 3mall-seeded, narrow leaved C. sativa (SS) from 
India and Pakistan is not so significantly distinct from C saliva 
(S) as is C indica. No formal infraspecific status is proposed for 
those small-seeded plants, but further study is warranted. 

The three species, C. sativa. C. indica, and C ruderalis, are well 
defined in leaflet width /length ratios, and the latter two are also 
distinguished from C. sativa in their oblanceolate leaflets 
(WP/L). Leaf morphology groupings reported here are 
compatible for those of the holotypes of C. sativa and C indica; 
the type specimen of C ruderalis was not available for 

measurement. 

Modal leaflet number for C sativa was 7 with a mean of 6.35. 
Leaves of C indica had a mode of 9 (mean, 8.20), and C ruderalis 
had a modal leaflet number of 5 (mean, 4.59). No significant 
differences were found in leaf morphology between sexes of a 
given species, but in a few populations the female plants had 
wider leaflets than did the males. 

Leaf character sets were generally reinforcing: i.e., leaves of C. 
indica that were unusually narrow and thereby somewhat like 
those of C sativa were also very oblanceolate. The most nearly 
intermediate leaf morphology was found in a stout Japanese 
cultivar of C sativa with W/L - .143 and WP/L = .524. It was 
unique in having smooth stalks (few if any trichomes) and no 
THC content. Multivariate analysis would have dramatized the 
distinctness of the foliar characteristics of the species more 
completely, but /-tests were considered ample. 

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Table 1. Mean measurements for leaf morphology in Cannabis. 

Collection Leaf Features 

Group set L (mm) W/L WP L 



C. saliva (S) 


1976 


131. 7 


.133 


.460 




1972 


128.5 


.108 


.420 




wild 


114.2 


.110 


.423 


C. saliva (SS) 


1976 


93.0 


.101 


.505 




1972 


90.9 


.094 


.422 




wild 


65.4 


.097 


.402 


C ruderalis (R) 


1976 


67.1 


.163 


.536 




1972 










wild 


59.5 


,214 


.517 


C indica (I) 


1976 


143.3 


.207 


.578 




1972 


118.3 


.172 


.560 




wild 


83.6 


.214 


.579 



•See text and Fig. I for key to leaf features; C. ruderalis was not grown in the garden in 
1972. 



Table 2. Combined set mean data* for 
leaf morphology in Cannabis 



Leaf Feature C. saliva (S) C. sativa (SS) C. ruderalis (R) C. indica (I) 



125.9 78.8 61.8 II7.0 



W/L A05 ^94 .203 .182 

WP/L .436 .426 .523 .565 



• Means connected with — are not significantly different (p = >. I) 

Means connected with are significantly different at p = .1-.05 

Means not connected are very significantly different at p = <.01 



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w 








^^'r 



Fig. L Tracing of leaf of C indica from plant grown in garden from seed 
from Afghanistan (Anderson 4390; garden accession AF-G), showing 
measurements made on central leaflet. L — leaflet length, W = width, and WP = 
length to widest point of leaflet. The ratios of W/L and WP/ L for the various 
sets of plants are given in Tables 1 and 2. 



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Fig. 2. Growth patterns in Cannabis species; S= C miiva, I — C indica, 
and K — C. ruderalis. Plants drawn with representative heights of eight, four, 
and tw^o feet, respectively. 



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DISCUSSION 

Differing views on the taxonomy of Cannabis have generated 
much interest — perhaps more so in forensic circles than in 
scientific settings. Still, species delimitations should be deter- 
mined on the plant biology rather than on legal implications or 
societal needs (cX, Small, 1975). 

Leaflet morphology and number do correlate well with the 
distinctive growth forms of the species (Fig. 2), Three major 
groupings of features are found, and each represents a named 
species. They are as follows: 

1 . Cannabis sativa: Plants relatively tall, 5- 1 8 feet tall or more, 
laxly branched; leaves usually palmately compound with (3) 
5-7 (11) leaflets, central leaflet lanceolate with W/L ratio 
(.05) .09. 12 (.15). Environmentally induced unifoliate 
(simple) leaves of garden plants from Thailand were also 
narrowly lanceolate. 

2. Cannabis indica: Plants short, 2-4 feet tall, pyramidal, 
compactly branched; leaflets (5) 7-11 (13), central leaflet 
oblanceolate with W/L ratios (.14) .17-. 21 (.35). 

3. Cannabis ruderalis: Plants (female) very short, 0.5-2 feet 
tall, usually unbranched; leaflets 3-5 (7), central leaflet 
elliptic with W/L ratio (.10) .16.21 (.45). 

Plant heights given are those under normal conditions; C. sativa 
can be photo-induced to flower in the seedling stage. These three 
complements of characteristics are found in wild or weedy 
settings and are maintained in the uniform garden. None of the 
features appear to be simply environmental variants. 

Features of wood anatomy also distinguished C. sativa and C 
indica (Anderson, 1974). Study of the woods of garden samples is 
nearly complete. The additional samples are corroborative for 
those two species, and C ruderalis wood is intermediate to that of 
the other two species but distinctive. 

Other features such as plant odor, leaf color and leaflet 
serration pattern may prove to be of taxonomic value, but they 
were not quantified in this study. Similarly, seed (achene) features 
may be helpful, but I did not collect seeds. Earlier taxonomic 

67 



applications of achene data are contradictory (Emboden, 1974; 
Small and Cronquist, 1976). 

Recent proponents of the monotypic view of Cannabis (Small 
and Conquist, 1 976) emphasize chemical data and interfertility of 
the plants. Data from hybridization experiments are sometimes 
over-emphasized. Those which can be achieved through artificial 
hybridization in the garden or greenhouse often give an 
exaggerated view of biological interactions among natural 
populations. In general, interspecific hybridization is a relatively 
frequent phenomenon (Knoblock, 1959), especially so in wind- 
pollinated species such as Cannabis, The ability to hybridize or 
not is not recommended as a sole or major species criterion, 
because the degree of fertility among interspecific hybrids varies 
widely (Stace, 1975). This is particularly true for many weedy 
plants (like Cannabis); Baker (1972) states: "A full spectrum of 
interspecific hybridization can be seen in the world's weed flora, 
from the formation of sterile F| hybrids to the production of 
vigorous, fertile amphidiploids or significant introgression.'' 

Species of Cannabis are not mutually exclusive in their 
cannabinoid content, and cannabinoids are known to fluctuate in 
quantity and composition during the life cycle of the plant. 
Consequently, a study group sponsored by the United Nations 
Narcotics Laboratory (1976) stated that "cannabinoid composi- 
tion can serve only as a limited chemotaxonomic tool" Turner er 
aL (1973) demonstrated that cannabinoid composition is not 
stable in stored plant material, and Turner (pers. comm.) has 
noted daily fluctuations in cannabinoid content in living plants. 
Therefore, a single plant might be classified with Small and 
Cronquist's key ( 1976) as C sativa ssp, sativa at one time of day 
and as C sativa ssp, indica at another time of day! Clearly the use 
of chemical data as primary taxonomic criteria (Small and 
Cronquist, 1976) is neither practical nor natural and has been 
duly criticized by Emboden (1977). 

Judging from SmalTs annotations on herbarium sheets, his 
predilection to classify plants by intoxicant ability and /or 
geographical distribution has resulted in placing many plants of 
C sativa in with C, indica. Consequently, the two groups would 
then not represent distinctive morphological forms (perhaps this 
contributed to his recognition of the groups as subspecies rather 

68 



than species). My circumscription of C indka is narrower than 
that which constitutes C sativa ssp. indica (Lam.) Small & 
Cronquist. Thus, it should be noted that studies based on material 
supplied by Small (such as Clark and Bohm, 1979) would reflect 
his wider interpretation of C indica as a subspecies of C sativa. 
The genus Cannabis might best be described on morphology 
rather than chemical composition as having three closely related 
but distinct species: C sativa, C indica, and C ruderalis. One 
species, C sativa, itself is extremely variable, having been 
domesticated by early man for use as food, fibre, oil, medicine, 
and hallucinogen. 



LITERATURE CITED 



Anderson, L. C. 1974. A study of systematic wood anatomy in dmnahis. 

Harvard Univ. Bot. Mus. Lean. 24: 29 36. 
Baker. H. G, 1972. Migration of weeds. In Taxonomy, Phytogeography, and 

Evolution (D. FU Valentine, ed.). Academic Press, New York. 
Clark, M. N. and B. A. Rohm. 1979. Elavonoid variation in Cannabis L. Bot. J, 

Linn. Soc. 79: 249 257. 
Emboden, W. A. 1974. Camiahis—'d polytypic genus. Econ. Bot. 28: 304 310. 
Emboden, W. A. 1977. A taxonomv of Cannabis. Taxon 26: 1 10. 
Knoblock, 1, W, 1959. A preliminary estimate of the importance of h)bridi/.ation 

in speciation. Bull Torr. Bot. Club 86: 296 299, 
Quimby, M. W., N. J. Doorenbos, C. E. Turner, and A. Masoud. 1973. 

Mississippi-grown marihuana-Cannahis saliva. Cultivation and observed 

morphological variations. Econ. Bot. 27: 117 127. 
Schultes, R. E.. W. M. Klein, T, Plowman, and T. E. Lockwood. 1974. 

Cannabis: an example of taxonomic neglect. Harvard Univ. Bot. Mus. 

Leafl. 23: 337 367. 
Small, E. 1975. On toadstool soup and legal species of Cannabis. PL Sci. Bull 

21: 34-39. 
Small E, and A. Cronquist. 1976. A practical and natural taxonomy for 

Cannabis. Taxon 25: 405 435. 
Stace, C. A. 1975. Hybridization and the Elora of the British Isles. Academic 

Press, New York. 
Turner, C E., K. W. Hadley, P. S. Fetterman, \. J. Doorenbos, M. W. Quimby, 

and C. Walter. 1973. Constituents of Cannabis saliva l.^ IV: Stability of 

cannabinoids in stored plant material. J. Pharm. Sci. 62: 1601 1605. 
United Nations. 1976. The botany and chemotaxonomy of Cannabis. United 

Nations document MNAR 15 1976, Geneva. 



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